package 二叉树;

import java.util.Stack;

/**
 * 700. Search in a Binary Search Tree
 * https://leetcode.com/problems/search-in-a-binary-search-tree/
 *
 * Given the root node of a binary search tree (BST) and a value.
 * You need to find the node in the BST that the node's value equals the given value.
 * Return the subtree rooted with that node.
 * If such node doesn't exist, you should return NULL.
 *
 * For example,
 *
 * Given the tree:
 *         4
 *        / \
 *       2   7
 *      / \
 *     1   3
 *
 * And the value to search: 2
 * You should return this subtree:
 *
 *       2
 *      / \
 *     1   3
 * In the example above, if we want to search the value 5, since there is no node with value 5, we should return NULL.
 *
 * Note that an empty tree is represented by NULL, therefore you would see the expected output (serialized tree format) as [], not null.
 */
public class E_700_二叉搜索树中的搜索 {
    /**
     * 递归
     */
    public TreeNode searchBST(TreeNode root, int val) {
        if (root == null) return null;

        if (root.val == val) {
            return root;
        } else if (root.val > val) {
            return searchBST(root.left, val);
        } else {
            return searchBST(root.right, val);
        }
    }

    /**
     * 迭代
     */
    public TreeNode searchBST2(TreeNode root, int val) {
        while (root != null) {
            if (root.val == val) {
                return root;
            } else if (root.val > val) {
                root = root.left;
            } else {
                root = root.right;
            }
        }
        return root;
    }
}
